A Signal-to-interference ratio (SIR) measuring apparatus in a multiple antenna high data rate packet transmission system measures signal energy to interference energy ratio by using pilot signals that are orthogonal to each other between antennas signals and used by a receiver for separating the signals transmitted from all of the transmitting antennas from each other. The SIR measuring apparatus comprises a signal energy measuring unit, an interference energy measuring unit and a SIR measuring unit. The signal energy measuring unit measures signal energy by synthesizing after coherently integrating and non-coherently integrating values that are obtained by correlating a received signal with pilot patterns equal to the pilot patterns of transmitted antenna signals, respectively. The interference energy measuring unit measures interference energy by coherently integrating and non-coherently integrating after correlating the received signal with another pattern that is orthogonal to the pilot patterns of the transmitted antenna signals but is not transmitted. The SIR measuring unit measures SIR by using the measured signal energy and the measured interference energy.